1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, it relates to a semiconductor device having a metal electrode interconnection film which is applied to a large-scale semiconductor integrated circuit (LSI).
2. Description of the Prior Art
FIGS. 1 and 2 are sectional views showing an example of a conventional semiconductor device which is applied to an LSI.
With reference to FIG. 1, description is now made on the structure of the conventional semiconductor device. Referring to FIG. 1, insulating films 1a and 2b for separating respective elements are formed on a silicon substrate 1 and an impurity diffusion layer 5 is formed in a region defined by the insulating films 2a and 2b. Thereafter another impurity diffusion layer 9 is formed in this region through an ion implantation method or a thermal diffusion method. Interlayer insulating films 6a and 6b are formed on the insulating films 2a and 2b and the impurity diffusion layer 5, and an aluminum alloy film 11 is formed thereon to have a contact hole portion 7 whose bottom is in contact with the surface of the impurity diffusion layer 5.
Description is now made on the function of the conventional semiconductor device as shown in FIG. 1. The silicon substrate 1 and the impurity diffusion layer 5 are in P-N junction with each other to form a path for electric signals, which path corresponds to source/drain layers of a MOS element. The impurity diffusion layer 5 is electrically in contact with the aluminum alloy film 11 serving as an upper electric signal path at the bottom of the contact hole portion 7. The other impurity diffusion layer 9 is adapted to improve the P-N junction in peak inverse voltage, particularly in surge voltage, and is formed by introducing N-type impurities into the P-type semiconductor silicon substrate 1 through ion implantation or thermal diffusion. Even if the contact hole portion 7 is deviatingly formed in a region lapping over the insulating layer 2a or 2b, in which region no impurity diffusion layer 5 is formed to provide P-N junction, the other impurity diffusion layer 9 is self-alignedly formed through the contact hole portion 7 to provide P-N junction.
However, the conventional semiconductor device of the aforementioned structure has various disadvantages as follows:
(1) In recent years, elements are implemented with higher density of integration, whereby semiconductor devices must be vertically reduced in size in addition to having a fine structure in the horizontal direction. In other words, it is important to form impurity diffusion layers reduced in depth in order to retain/improve characteristics of the elements. In the conventional semiconductor device as shown in FIG. 1, however, the impurity diffusion layers are increased in sheet resistivity by a reduction in depth.
(2) The impurity diffusion layer 5 of the conventional semiconductor device as shown in FIG. 1 is electrically in contact with the aluminum alloy film 11, and in such case, contact resistance is essentially higher than that between metal layers.
(2) In heat treatment after formation of the aluminum alloy film 11, counter diffusion takes place between aluminum (Al) in the aluminum alloy film 11 and silicon (Si) in the impurity diffusion layer 5 to cause the so-called "punch-through" of "spike" phenomenon breaking the original P-N junction. In order to prevent such a phenomenon, a supersaturated concentration of Si is generally added in the aluminum alloy film 11. However, such added Si is deposited on the impurity diffusion layers 5 and 9 in portions close to the bottom of the contact hole portion 7 in a cooling step after the said heat treatment, as shown by 12a and 12b in FIG. 2. The effective contact opening area between the aluminum alloy film 11 and the impurity diffusion layer 5 is decreased by the deposited Si portions 12a and 12b, leading to an increase in contact resistance. Further, the deposited Si portions 12a and 12b including Al are of P types to form P-N junction with the N-type impurity diffusion layers 5 and 9, whereby the contact resistance is further increased when currents flow in the reverse bias direction.
(4) Even if Si is added in the aluminum alloy film 11 as hereinabove described, the said "punch-through" or "spike" phenomenon is caused to break the original P-N junction when Si is unevenly distributed or the heat treatment is performed at a high temperature for a long time.
The aforementioned various disadvantages are particularly serious these days with a decrease in the diameter of contact holes and a reduction in the depth of the impurity diffusion layers for highly integrating the elements of fine structure. "The Use of Titanium-Based Contact Barrier Layers in Silicon Technology" by C. Y. Ting and M. Wittmer in Thin Solid Films, 96 (1982) pp. 327-344 disclosed a technique of providing a contact barrier layer of only molybdenum silicide (MoSi.sub.2) or only titanium silicide (TiSi.sub.2) between an aluminum alloy layer and a silicon substrate in order to improve the aforementioned points, whereas such technique is still insufficient in various points such as chemical resistance.